Flow Field Predictions of Bluff Body Introduced Micro Combustor

A swirling double concentric jet is commonly used for nonpremixed gas burner application for safety reasons and to improve the combustion performance. Fuel is generally spurted at the central jet while the annular coflowing air is swirled. They are normally separated by a blockage disk where the bluff-body effects further enhance the recirculation of hot gas at the reaction zone. This paper aims to experimentally investigate the behavior of flame and flow in a double concentric jet combustor when the fuel supply is acoustically driven. Laser-light sheet assisted Mie scattering method has been used to visualize the flow, while the flame lengths were measured by a conventional photography technique. The fluctuating velocity at the jet exit was measured by a two-component laser Doppler velocimeter. Flammability and stability at first fuel tube resonant frequency are reported and discussed. The evolution of flame profile with excitation level is presented and discussed, together with the reduction in flame length. The flame in the unforced reacting axisymmetric wake is classified into three characteristic modes, which are weak swirling flame, lifted flame, and transitional reattached flame. These terms reflect their primary features of flame appearances, and when the acoustic excitation is applied, the flame behaviors change with the excitation frequency and amplitude. Four additional characteristic modes are identified; e.g., at low excitation amplitudes, wrinkling flame with a blue annular film is observed because the excitation induces vortices in the central fuel jet and hence gives rise to the wrinkling of flame. The central jet vortices become larger with the increase in excitation amplitude and thus lead to a wider and shorter flame. If the excitation amplitude is increased above a certain value, the central jet vortices change the rotation direction and pacing with the annular jet vortices. These changes in the flow field induce large turbulent intensity and mixing and therefore make the flame looks blue and short. Further increase in the excitation amplitude would lift the flame because the flow field would be dramatically modified.

Download Full-text

Bionic shape design of electric locomotive and aerodynamic drag reduction

Archives of Transport ◽

10.5604/01.3001.0012.8369 ◽

2018 ◽

Vol 4 (48) ◽

pp. 99-109

Author(s):

Zhenfeng WU ◽

Yanzhong HUO ◽

Wangcai DING ◽

Zihao XIE

Keyword(s):

Flow Field ◽

Drag Reduction ◽

Bluff Body ◽

Aerodynamic Drag ◽

Geometric Characteristic ◽

Shape Design ◽

Shape Optimisation ◽

Electric Locomotive ◽

Geometric Models ◽

Characteristic Lines

Bionics has been widely used in many fields. Previous studies on the application of bionics in locomotives and vehicles mainly focused on shape optimisation of high-speed trains, but the research on bionic shape design in the electric locomotive field is rare. This study investigated a design method for streamlined electric locomotives according to the principles of bionics. The crocodiles were chosen as the bionic object because of their powerful and streamlined head shape. Firstly, geometric characteristic lines were extracted from the head of a crocodile by analysing the head features. Secondly, according to the actual size requirements of the electric locomotive head, a free-hand sketch of the bionic electric locomotive head was completed by adjusting the position and scale of the geometric characteristic lines. Finally, the non-uniform rational B-splines method was used to establish a 3D digital model of the crocodile bionic electric locomotive, and the main and auxiliary control lines were created. To verify the drag reduction effect of the crocodile bionic electric locomotive, numerical simulations of aerodynamic drag were performed for the crocodile bionic and bluff body electric locomotives at different speeds in open air by using the CFD software, ANSYS FLUENT16.0. The geometric models of crocodile bionic and bluff body electric locomotives were both marshalled with three cars, namely, locomotive + middle car + locomotive, and the size of the two geometric models was uniform. Dimensions and grids of the flow field were defined. And then, according to the principle of motion relativity, boundary conditions of flow field were defined. The results indicated that the crocodile bionic electric locomotive demonstrated a good aerodynamic performance. At the six sampling speeds in the range of 40–240 km/h, the aerodynamic drag coefficient of the crocodile bionic electric locomotive decreased by 7.7% on the average compared with that of the bluff body electric locomotive.

Download Full-text

Smart Passive Control of Thermoacoustic Instability in a Bluff-Body Stabilized Combustor: A Lagrangian Analysis of Critical Structures

Volume 4B: Combustion, Fuels, and Emissions ◽

10.1115/gt2020-16073 ◽

2020 ◽

Author(s):

C. P. Premchand ◽

Manikandan Raghunathan ◽

Midhun Raghunath ◽

K. V. Reeja ◽

R. I. Sujith ◽

...

Keyword(s):

Wavelet Transform ◽

Flow Field ◽

Heat Release ◽

Shear Layer ◽

Heat Release Rate ◽

Release Rate ◽

Sound Production ◽

Bluff Body ◽

Passive Control ◽

Thermoacoustic Instability

Abstract The tonal sound production during thermoacoustic instability is detrimental to the components of gas turbine and rocket engines. Identifying the root cause and controlling this oscillatory instability would enable manufacturers to save in costs of power outages and maintenance. An optimal method is to identify the structures in the flow-field that are critical to tonal sound production and perform control measures to disrupt those “critical structures”. Passive control experiments were performed by injecting a secondary micro-jet of air onto the identified regions with critical structures in the flow-field of a bluff-body stabilized, dump, turbulent combustor. Simultaneous measurements such as unsteady pressure, velocity, local and global heat release rate fluctuations are acquired in the regime of thermoacoustic instability before and after control action. The tonal sound production in this combustor is accompanied by a periodic flapping of the shear layer present in the region between the dump plane (backward-facing step) and the leading edge of the bluff-body. We obtain the trajectory of Lagrangian saddle points that dictate the flow and flame dynamics in the shear layer during thermoacoustic instability accurately by computing Lagrangian Coherent Structures. Upon injecting a secondary micro-jet with a mass flow rate of only 4% of the primary flow, nearly 90% suppression in the amplitude of pressure fluctuations are observed. The suppression thus results in sound pressure levels comparable to those obtained during stable operation of the combustor. Using Morlet wavelet transform, we see that the coherence in the dominant frequency of pressure and heat release rate oscillations during thermoacoustic instability is affected by secondary injection. The disruption of saddle point trajectories breaks the positive feedback loop between pressure and heat release rate fluctuations resulting in the observed break of coherence. Wavelet transform of global heat release rate shows a redistribution of energy content from the dominant instability frequency (acoustic time scale) to other time scales.

Download Full-text

Simulation of Two-Dimensional Turbulent Recirculating Flow Field Behind a V-Shaped Bluff Body

ASME 1994 International Computers in Engineering Conference and Exhibition ◽

10.1115/cie1994-0459 ◽

1994 ◽

Author(s):

Z. Gu ◽

M. A. R. Sharif

Keyword(s):

Flow Field ◽

Bluff Body ◽

Flame Stabilization ◽

Bluff Bodies ◽

Two Dimensional ◽

Combustion Chambers ◽

Recirculating Flow ◽

Conservative Form ◽

Curvilinear Grid ◽

Predictor Corrector

Abstract The two-dimensional turbulent recirculating flow fields behind a V-shaped bluff body have been investigated numerically. Similar bluff bodies are used in combustion chambers for flame stabilization. The governing transport equations in conservative form are solved by a pressure based predictor-corrector method. The standard k-ϵ turbulence closure model and a boundary fitted multi-block curvilinear grid system are used in the computation. The code is validated against turbulent flow over a backward facing step problem. The predicted flow field behind the bluff body is also compared with experiment. It is found that while the qualitative features of the flow are well predicted, there is quantitative disagreement between the measurement and prediction. This disagreement can be partially attributed to the k-ϵ turbulence model which is known to be inadequate for recirculating flows. Parametric investigation of the flow field by varying the shape and size of the bluff body is also performed and the results are reported.

Download Full-text

Numerical and Experimental Study on Soot Accumulation on the Wall of Falling Fuel Film Micro-Combustor

2010 14th International Heat Transfer Conference, Volume 3 ◽

10.1115/ihtc14-22093 ◽

2010 ◽

Author(s):

Ning Mei ◽

Xiaoyan Wang ◽

Hongming Zhao ◽

Yan Li ◽

Hongyu Si

Keyword(s):

Flow Field ◽

Combustion Chamber ◽

Turbulence Model ◽

Complex Structure ◽

Flow Distribution ◽

Experimental Results ◽

Fuel Film ◽

Numerical Result ◽

Different Diameters ◽

Micro Combustor

Fluid flow contributes much to fuel-air mixture formation in a micro-combustor, the RNG k-ε turbulence model was used to simulate the cold flow field of a falling fuel film microcombustor, and comparison was made between numerical result and experimental results. It is shown that the RNG k-ε turbulence model translated the flow field of a complex structure micro-combustor and the soot accumulation on the wall of combustion chamber. The experimental results showed that soot accumulation occurs in vortex backflow area near the wall of combustion chamber and the numerical methods is helpful for understanding the way of soot accumulation in the wall of combustion chamber. Therefore, modifications on the flow field with different diameters and entrance direction of the air flow into the primary combustion chamber were made. The numerical simulation of flow distribution showed that the flow field of micro-combustor could be ideal for eliminated soot accumulation.

Download Full-text

The effect of the blockage ratio on the blow-off limit of a hydrogen/air flame in a planar micro-combustor with a bluff body

International Journal of Hydrogen Energy ◽

10.1016/j.ijhydene.2013.06.100 ◽

2013 ◽

Vol 38 (26) ◽

pp. 11438-11445 ◽

Cited By ~ 41

Author(s):

Aiwu Fan ◽

Jianlong Wan ◽

Yi Liu ◽

Boming Pi ◽

Hong Yao ◽

...

Keyword(s):

Bluff Body ◽

Blockage Ratio ◽

Micro Combustor

Download Full-text

Flow Field Characterization of an Angled Supersonic Jet Near a Bluff Body

28th AIAA Applied Aerodynamics Conference ◽

10.2514/6.2010-4829 ◽

2010 ◽

Author(s):

John Wolter ◽

Robert Childs ◽

Mark Wernet ◽

Andrea Nelson ◽

John Melton

Keyword(s):

Flow Field ◽

Bluff Body ◽

Supersonic Jet

Download Full-text

Partially Premixed Flame Stabilization in the Presence of a Combined Swirl and Bluff Body Influenced Flowfield: An Experimental Investigation

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4046965 ◽

2020 ◽

Vol 142 (7) ◽

Author(s):

Rajesh Sadanandan ◽

Aritra Chakraborty ◽

Vinoth Kumar Arumugam ◽

Satyanarayanan R. Chakravarthy

Keyword(s):

Flow Field ◽

Bluff Body ◽

Reverse Flow ◽

Fluid Dynamic ◽

Thermal Power ◽

Swirl Flow ◽

Flame Stabilization ◽

Dynamic Strain ◽

Low Velocity ◽

Divergent Flow

Abstract Optical and laser diagnostic measurements in a nonpremixed model gas turbine (GT) burner have been performed to investigate the effect of an increase in thermal power on the flame stabilization. The model GT burner has a large bluff body base with an annular swirl region, leading to a convergent-divergent flow field at the burner exit. Under the investigated conditions, the flame stabilizes predominantly in the diverging section characterized by the swirl flow with a central recirculation zone. With increasing thermal power, the reverse flow of hot burned gases is strengthened, with the hydroxyl radical (OH) planar laser induced fluorescence (PLIF) images indicating an increase in the temperature of the burned gases. The preferred flame stabilization location coincides with the inner shear layer between the reactant inflow and the reverse flow of hot burned gases. At high thermal power, the flame seems to stabilize in regions of high fluid dynamic strain rate, highlighting the influence of the reverse flowing burned gases in the evolution of the flammable mixture upstream. However, simultaneous and time-resolved measurements of the flow-field and scalar field are needed for direct quantification of this. The results are in agreement with the flame stabilization theories based on partial fuel-air mixing and streamline divergence. The flow is seen to decelerate upstream of the flame front and the flame stabilizes in a region of low velocity, created as a result of heat release diverging the streamlines ahead of it.

Download Full-text